The San Bernardino shooting is the second mass shooting today and the 355th this year

Police in San Bernardino, Calif., said heavily armed gunmen killed 14 people and injured 21 others during a holiday party for county employees. Here's what we know about the mass shooting. (The Washington Post)

The San Bernardino shooting is the 355th mass shooting this year, according to a mass shooting tracker maintained by the Guns Are Cool subreddit. The Reddit tracker defines mass shootings as incidents in which four or more people, including the gunman, are killed or injured by gunfire.

The Mass Shooting Tracker is different from other shooting databases in that it uses a broader definition of mass shooting — the old FBI definition focused on four or more people killed as part of a single shooting.

Speaking after the Colorado Springs shooting last week, President Obama urged Americans to not let this type of violence "become normal." But the data show that this type of incident already is normal. There have been more mass shootings than calendar days so far this year.

What the investigation and scene of the shooting in San Bernardino look like

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The attackers were killed in a confrontation with police after a shooting at the nonprofit Inland Regional Center that left 14 dead.

Caption

The attackers were killed in a confrontation with police after a shooting at the nonprofit Inland Regional Center that left 14 dead.

Dec. 11, 2015A diver searches for evidence in the San Bernardino, Calif., shooting massacre that may have been thrown into Seccombe Lake. Syed Farook and his wife, Tashfeen Malik, killed 14 people and injured 21 at the Inland Regional Center.David Mcnew/Getty Images